SiC Micro Research Articles

Morphological and Wear behaviour of new Al-SiCmicro-SiCnano hybrid nanocomposites fabricated through powder metallurgy

In the present work, aluminium matrix composites reinforced with 10 wt% SiC micro particles along with x% SiC nano particles (x = 0, 1, 3, 5 and 7 wt%) were fabricated through powder metallurgy. The fabricated hybrid composites were characterized by x-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectrum (EDS) and elemental mapping. The relative density, hardness and wear behaviour of all hybrid nanocomposites were studied. The influence of various control factors like SiC reinforcement, sliding distance (300, 600, 900 and 1200 m) and applied load (20, 30 and 40 N) were explored using pin-on-disc wear apparatus. The uniform distribution of micro and nano SiC particles in aluminium matrix is confirmed by elemental maps. The hardness and wear test results showed that properties of the hybrid composite containing 5 wt% nano SiC was better than other hybrid composites. Additionally, the wear loss of all hybrid nanocomposites increases with increasing sliding distance and applied load. The identification of wear phenomenon were studied through the SEM images of worn surface.

Simultaneous improvement of mechanical strength, ductility and corrosion resistance of stir cast Al7075-2% SiC micro- and nanocomposites by friction stir processing

Present work investigates the mechanisms of simultaneous improvement of tensile properties, wear properties and corrosion resistance of stir cast Al7075–2wt.% SiC micro- and nanocomposites through microstructural refinement by friction stir processing (FSP). Optical, scanning and transmission electron microscopy were used to investigate the microstructural evolution. After the FSP, the nanoparticles reinforced composite showed better mechanical properties than that of the microparticles reinforced composite. Tensile strength ( >3 times) and wear resistance were found to increase significantly with simultaneous enhancement of the ductility (10 times). The improvement is ascribed to the grain size reduction, distribution of SiC nanoparticles uniformly within the matrix, increase particle-matrix interface characteristics and elimination of casting defects such as porosity after the FSP. The corrosion potentials of the as-cast composites were found to shift towards noble direction after the FSP. Enhancement of corrosion resistance after the FSP is attributed to the decrease in the heterogeneity on the surface and uniform dispersion of the reinforced particles, which reduced the effective active surface area exposed to the corrosive solution. All such beneficial effects were found to be superior for the nanoparticles reinforced composite due to the improved particle/matrix interface characteristics and dispersion strengthening.

Effect of the silicon-carbide micro- and nanoparticle size on the thermo-elastic and time-dependent creep response of a rotating Al–SiC composite cylinder

The history of stresses and creep strains of a rotating composite cylinder made of an aluminum matrix reinforced by silicon carbide particles is investigated. The effect of uniformly distributed SiC micro- and nanoparticles on the initial thermo-elastic and time-dependent creep deformation is studied. The material creep behavior is described by Sherby’s constitutive model where the creep parameters are functions of temperature and the particle sizes vary from 50 nm to 45.9 μm. Loading is composed of a temperature field due to outward steady-state heat conduction and an inertia body force due to cylinder rotation. Based on the equilibrium equation and also stress-strain and strain-displacement relations, a constitutive second-order differential equation for displacements with variable and time-dependent coefficients is obtained. By solving this differential equation together with the Prandtl–Reuss relation and the material creep constitutive model, the history of stresses and creep strains is obtained. It is found that the minimum effective stresses are reached in a material reinforced by uniformly distributed SiC particles with the volume fraction of 20% and particle size of 50 nm. It is also found that the effective and tangential stresses increase with time at the inner surface of the composite cylinder; however, their variation at the outer surface is insignificant.

Bioinspired high toughness graphene/ZrB2 hybrid composites with hierarchical architectures spanning several length scales

Natural bioinspired hierarchically ordered architectures from the nanoscale to the macroscale are achieved in graphene/ZrB2 hybrid composites to improve their toughness using graphene oxide. Two types of films containing different volumes of graphene oxide are self-assembled with ZrB2 or SiC micro particles through a vacuum-assisted filtration method. Scanning electron microscopy images show that ceramic particles are homogeneously distributed in a continuous multilayer graphene oxide network, forming a nano-micro hierarchical structure. Tensile tests are employed to test the strength of these films. The spark plasma sintering method is utilized to construct micro-macro structural order through densifying two types of alternately stacked films containing different volumes of graphene oxide. Indentation tests reveal alternately compressive and tensile layers are achieved after the sintering process. By combining different structural features spanning several length scales, the composites exhibit a unique combination of high strength (522 MPa) and toughness (9.5 MPa m0.5); in particular, the fracture toughness is more than double that of the composite without the hierarchical architecture. The toughening mechanisms are also analyzed at different length scales. This bioinspired material-independent approach should be employed in the designing and processing of materials for structural, high-temperature and energy related applications.

The effect of SiC powder mixing electrical discharge machining on white layer thickness, heat flux and fatigue life of AISI D2 die steel

This paper deals with studying the effect of powder mixing electrical discharge machining (PMEDM) parameters using copper and graphite electrodes on the white layer thickness (WLT), the total heat flux generated and the fatigue life. Response surface methodology (RSM) was used to plan and design the experimental work matrices for two groups of experiments: for the first EDM group, kerosene dielectric was used alone, whereas the second was treated by adding the SiC micro powders mixing to dielectric fluid (PMEDM). The total heat flux generated and fatigue lives after EDM and PMEDM models were developed by FEM using ANSYS 15.0 software. The graphite electrodes gave a total heat flux higher than copper electrodes by 82.4%, while using the SiC powder and graphite electrodes gave a higher total heat flux than copper electrodes by 91.5%. The lowest WLT values of 5.0 µm and 5.57 µm are reached at a high current and low current with low pulse on time using the copper and graphite electrodes and the SiC powder, respectively. This means that there is an improvement in WLT by 134% and 110%, respectively, when compared with the use of same electrodes and kerosene dielectric alone. The graphite electrodes with PMEDM and SiC powder improved the experimental fatigue safety factor by 7.30% compared with the use of copper electrodes and by 14.61% and 18.61% compared with results using the kerosene dielectric alone with copper and graphite electrodes, respectively.

Preparation and Characterization of SiC/SiC Micro Ceramic Matrix Composites

SiC continuous fiber reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) and SiC fiber reinforced SiC micro ceramic matrix composites (SiCf/SiC micro-CMCs) were prepared through polymer impregnation pyrolysis (PIP) progress, then the structures, mechanical properties and forming mechanisms of SiCf/SiC CMCs were investigated. Results showed that volume shrinkage of SiC matrix occurred, and pyrolysates with bamboo-like layered structure were attached to the surface of SiC multifilament gradually. Furthermore, the mechanical properties of SiCf/SiC micro-CMCs were consistent with SiCf/SiC CMCs, so the PIP process parameters for the preparation of SiCf/SiC CMC might be optimized primarily through SiCf/SiC micro-CMCs, which could enhance the design and preparation efficiency of SiCf/SiC CMCs obviously.Key word: polymer impregnation pyrolysis progress, micro ceramic matrix composites, forming mechanism

Wear and scratch resistance characteristics of electrodeposited nickel-nano and micro SiC composites

Nickel-nano and micro Silicon carbide composites were electrodeposited on steel substrates. Sediment co-deposition technique was used in a conventional Watts bath with Tetra Methyl Ammonium Hydroxide (TMAH) as the surfactant. Deposits with varying volume% of SiC were obtained by varying the amount of SiC in bath and the operating conditions. Resistance of the composites to wear and scratch and their surface roughness were measured and compared. It is confirmed that, for a given volume% of the particles in the deposit, Ni–SiC, nano composites exhibit much lower wear loss and higher scratch resistance compared to Ni–SiC micro composites.

Effect of particle size and co-deposition technique on hardness and corrosion properties of Ni–Co/SiC composite coatings

Ni–Co/SiC alloy matrix composite coatings were electrodeposited in a modified Watt's bath containing micro and nano sized SiC particles by using conventional electro-co-deposition (CECD) and sediment co-deposition (SCD) techniques. The deposits were characterized using SEM, EDX and XRD analyses, and microhardness and potentiodynamic polarization measurements. The maximum incorporation of the SiC micro- and nano-particles was obtained using the SCD technique at deposition current densities of 2 and 3A/dm2, respectively. It was found that in the composite coatings, incorporation of SiC particles improves the microhardness of unalloyed Ni and Ni–Co alloy matrices. The nanocomposite coatings exhibit higher microhardness values than microcomposite ones. The potentiodynamic polarization measurements in 3.5% NaCl solution revealed that the corrosion resistance of the Ni–Co/SiC nanocomposite coatings is much higher than the Ni–Co alloy and Ni–Co/SiC microcomposite coatings. Moreover, corrosion resistance of Ni–Co/SiC nanocomposite coatings deposited by SCD technique is higher than the ones deposited by CECD technique. Corrosion resistance of the studied Ni–Co/SiC composite coatings was considerably affected by Co content, SiC particle size and content. Hardness enhancement was related to the structural features, and corrosion behavior was discussed based on the formation of corrosion micro cells, diminishing the effective metallic area, and increasing and hindering the corrosion paths.

Preparation of Cutting Inserts with Binder of UHCS

From studies on the Damascus steel, the manufacturing of ultra-high carbon content steel (UHCS) by powder metallurgy has been carried out in previous works. UHCSs have been manufactured mixing iron and graphite powders, uniaxial compacting, and sintering in vacuum atmosphere. Finally, they have been hot-rolled at relatively low temperatures using their superplasticity to obtain optimum properties. High hardness particles of SiC (micro and nanometric size) and diamond (with and without coating) were added to UHCS to produce inserts for cutting discs. Their mechanical properties have been studied through bending tests and hardness measurements. SEM observations have shown how the structure of the steel and the particles has been modified depending on the performed thermo-mechanical treatment. This way, it is possible to justify the effect of the addition of high hardness particles in the reduction of plasticity and wear resistance of the material.

SiC 마이크로 히터가 내장된 극한 환경용 NO 센서의 제작과 특성

This paper describes the fabrication and characteristics of a NO sensor using ZnO thin film integrated 3C-SiC micro heater based on polycrystalline 3C-SiC thin film of operation in harsh environments. The sensitivity, response time, and operating properties in high temperature and voltages of NO sensors based SiC MEMS are measured and analyzed. The sensitivity of device with pure ZnO thin film at the heater operating power of 13.5 mW (<TEX>$300^{\circ}C$</TEX>) is 0.875 in NO gas concentration of 0.046 ppm. In the case of Pt doping, the sensitivity of at power consumption of 5.9 mW (<TEX>$250^{\circ}C$</TEX>) was 1.92 at same gas flow rate. The ZnO with doped Pt was showed higher sensitivity, lower working temperature and faster adsorption characteristics to NO gas than pure ZnO thin film. The NO gas sensor integrated SiC micro heater is more strength than others in high voltage and temperature environments.

Effect of &lt;i&gt;In Situ&lt;/i&gt; Doped Nitrogen Concentrations on the Characteristics of Poly 3C-SiC Micro Resonators

This paper describes the characteristics of polycrystalline 3C-SiC micro resonators with 3 ×1017 - 1×1019 cm-3 in-situ N-doping concentrations. In this work, the 1.2 μm thick cantilevers and the 0.4 μm thick doubly-clamped beam micro resonators with various lengths were implemented using in-situ doping poly 3C-SiC thin films. The characteristics of the poly 3C-SiC micro resonators were evaluated using quartz actuator and optical read-out vibrometer under vacuum conditions at room temperature. The resonant frequencies of the SiC micro resonators decreased with doping concentrations owing to the reduction of the Young's modulus of the poly 3C-SiC thin films. It was confirmed that the resonant frequencies of the poly 3C-SiC micro- resonators are controllable by adjusting the doping concentrations.

Microstructure development, hardness, toughness and creep behaviour of pressureless sintered alumina/SiC micro–nanocomposites obtained by slip-casting

Al 2O 3–SiC micro–nanocomposites are much more resistant materials than monolithic alumina regarding some mechanical properties. In order to study the possibility of obtaining creep resistant alumina/SiC micro–nanocomposites using inexpensive forming methods, alumina 1 and 5 vol% SiC materials were produced by slip-casting and pressureless sintering. Well-densified alumina–SiC pressureless sintered materials were obtained at 1700 °C for 2 h and attained 97–99% of the theoretical density. The microstructure, hardness and toughness were examined and 4-point flexure creep tests were performed at 1200 °C and 100 MPa in air. Compared with pure alumina materials, the creep resistance, toughness and hardness were enhanced drastically in materials containing 5 vol% of SiC.

The Fabrication by using Surface MEMS of 3C-SiC Micro-heaters and RTD Sensors and their Resultant Properties

The electrical properties and the microstructure of nitrogen-doped poly 3C-SiC films used for micro thermal sensors were studied according to different thicknesses. Poly 3C-SiC films were deposited by LPCVD (low pressure chemical vapor deposition) at <TEX>$900^{\circ}C$</TEX> with a pressure of 4 torr using <TEX>$SiH_2Cl_2$</TEX> (100%, 35 sccm) and <TEX>$C_2H_2$</TEX> (5% in <TEX>$H_2$</TEX>, 180 sccm) as the Si and C precursors, and <TEX>$NH_3$</TEX> (5% in <TEX>$H_2$</TEX>, 64 sccm) as the dopant source gas. The resistivity of the poly SiC films with a 1,530 <TEX>${\AA}$</TEX> thickness was 32.7 <TEX>${\Omega}-cm$</TEX> and decreased to 0.0129 <TEX>${\Omega}-cm$</TEX> at 16,963 <TEX>${\AA}$</TEX>. The measurement of the resistance variations at different thicknesses were carried out within the <TEX>$25^{\circ}C$</TEX> to <TEX>$350^{\circ}C$</TEX> temperature range. While the size of the resistance variation decreased when the films thickness increased, the linearity of the resistance variation improved. Micro heaters and RTD sensors were fabricated on a <TEX>$Si_3N_4$</TEX> membrane by using poly 3C-SiC with a 1um thickness using a surface MEMS process. The heating temperature of the SiC micro heater, fabricated on 250 <TEX>${\mu}m$</TEX><TEX>${\times}$</TEX>250 <TEX>${\mu}m$</TEX> <TEX>$Si_3N_4$</TEX> membrane was <TEX>$410^{\circ}C$</TEX> at an 80 mW input power. These 3C-SiC heaters and RTD sensors, fabricated by surface MEMS, have a low power consumption and deliver a good long term stability for the various thermal sensors requiring thermal stability.

다결정 SiC 마이크로 공진기의 제작과 그 특성

This paper describes the resonant characteristics of polycrystalline SiC micro resonators. The thick polycrystalline 3C-SiC cantilevers with different lengths were fabricated using a surface micromachining technique. Polycrystalline 3C-SiC micro resonators were actuated by piezoelectric element and their fundamental resonance was measured by a laser vibrometer in vacuum at room temperature. For the long cantilevers, the fundamental frequency appeared at . The and long cantilevers have second mode resonant frequency at 857.5.kHz and 1.14.MHz, respectively. Therefore, polycrystalline 3C-SiC resonators are suitable for RF MEMS devices and bio/chemical sensor applications.

Machinability Investigation of Reaction-Bonded Silicon Carbide by Single-Point Diamond Turning

Reaction-bonded silicon carbide (RB-SiC) is a recently developed ceramic material with many merits such as low manufacturing temperature, dense structure, high purity and low cost. In the present paper, the precision machinability of RB-SiC was studied by microindentation and single-point diamond turning (SPDT) tests. The influence of depth of cut and tool feed rate on surface roughness and cutting force was investigated. Results showed that there was no clear ductile-brittle transition in machining behavior. The material removal mechanism involves falling of the SiC grains and intergranular microfractures of the bonding silicon, which prevents from large-scale cleavage fractures. The minimum surface roughness depends on the initial material microstructure in terms of sizes of the SiC grains and micro pores. This work preliminarily indicates that SPDT can be used as a high-efficiency machining process for RB-SiC.

Mechanical and anticorrosive properties of copper matrix micro- and nano-composite coatings

In the frame of the research domain of the production of metal matrix composite coatings, the aim of the present work was the production of copper electrodeposits containing micro- and nano-particles of SiC. The electrodeposition was carried out under dc conditions using a copper pyrophosphate plating bath into which micro- or nano-SiC particles were suspended. The composite coatings were tested and compared to pure copper coatings regarding their microstructure, mechanical and anticorrosive properties. The codeposition of SiC in the metal matrix changed the microstructure of the copper leading to improvement of both their mechanical and, in some cases, their protective properties. The Vickers microhardness presented an increase of about 35% and 61% in the case of SiC micro- and nano-particles incorporation while the increase of the abrasion resistance was 88% and 58%, respectively. The incorporation of the micro-particles lead to gaps formation among the SiC micro-particles and the metal matrix, thus lowering the resistance on both uniform and localized corrosion in comparison to the pure copper-coated specimens while the codeposition of SiC nano-particles produced deposits with higher resistance to both uniform and localized corrosion.

RECENT PROGRESSES OF APPLICATION-ORIENTED MEMS THROUGH INDUSTRY-UNIVERSITY COLLABORATION

MEMS research has been carried out through industry-university (Tohoku) collaboration for practical applications. Sophisticated devices such as electrostatically levitated rotational gyroscope, MEMS relay for wafer level packaging, array MEMS including multi-probe data storage and multi-column electron beam lithography system, small diameter fiber optic pressure sensor and SiC micro structure or glass press molding, have been developed. Electrical feedthroughs in glass play important role in the wafer level packaging and array MEMS. Materials such as conductive polymer for recording media, carbon nanotube for electron field emitter, SiC for harsh environment are used in these MEMS because of their unique features.

Development of High Performance SiC Fibers Derived from Polycarbosilane Using Electron Beam Irradiation Curing-A Review

Low-oxygen-content Si-C fibers (Hi-Nicalon) with 0.5 wt% oxygen were prepared from polycarbosilane with electron beam irradiation curing and pyrolysis. The thermal stability of the Hi-Nicalon fibers was significantly improved compared to Si-C-O fiber (Nicalon) with 12 wt% oxygen. However, creep deformation occurred in the Hi-Nicalon fiber at high temperatures, caused by SiC micro crystals and amorphous carbon. Then, stoichiometric and highly crystalline SiC fiber (Hi-Nicalon type S) was prepared from EB irradiation cured fiber by pyrolysis in a hydrogen gas flow. Type S fibers had high tensile modulus, excellent thermal stability, and creep resistance at high temperature. Hi-Nicalon and Hi-Nicalon type S fiber appear to be the best candidates for the reinforcement of ceramic matrix composites.

The size control of a SiC Micro Tube Synthesized by Radiation Process

The size control of a SiC Micro Tube Synthesized by Radiation Process

Nonuniformity of the Electrical Properties in SiC Micro Thermistors

Nonuniformity of the Electrical Properties in SiC Micro Thermistors